1. Field of the Invention
The present invention relates to a polarizing illumination device for uniformly illuminating a rectangular illumination area and the like by using polarized light beams polarized in the same direction, and to a projector using the polarizing illumination device. More particularly, the present invention relates to a structural technique for synthesizing light emitted from two light source sections while unifying the directions of polarization of the light.
2. Description of Related Art
A liquid crystal display device using a modulation device of a type that modulates a specific polarized light beam, such as a liquid crystal device, can utilize only one of two types of polarized light components included in light emitted from a light source. Therefore, there is a need to enhance light utilization efficiency in order to obtain a bright projection image. However, since a projector using only one light source has a limited ability to enhance light utilization efficiency, the amount of light has been increased by using a plurality of light sources as a way of obtaining a bright image.
However, when simply a plurality of light sources are arranged, the angle distribution of light for illuminating an illumination area is increased (the illumination angle is increased). Therefore, the amount of light in a given illumination angle is the same as that in the case where only one single light source is used. Consequently, in a projector in which the illumination angle is controlled by a projection system, the amount of light is not practically increased even when a plurality of light sources are used.
In addition, even if the amount of light is increased by using a plurality of light sources, when only one of two types of polarized light components, which are included in light emitted from the light sources, can be used, and half the light is wasted, which reduces the effectiveness by half.
It is an object of the present invention to provide a polarizing illumination device that is able to utilize both polarized light components by using a plurality of light sources, without increasing the illumination angle, and to provide a projector that is able to project a considerably bright projection image.
In order to achieve the above object, according to the present invention, there is provided a polarizing illumination device including:
a polarization separating optical element having a first polarization separating film for separating light incident from a first direction into two types of polarized light beams, emitting transmitted light in a third direction, and emitting reflected light in a fourth direction, and a second polarization separation film for separating light incident from a second direction into two types of polarized light beams, emitting reflected light in the fourth direction, and emitting transmitted light in a fifth direction;
a first light source section for allowing light to enter the polarization separating optical element from the first direction;
a second light source section for allowing light to enter the polarization separating optical element from the second direction;
a first condensing-and-reflecting optical element including a plurality of condensing-and-reflecting devices for approximately reversing the direction of travel of the light emitted in the third direction by the polarization separating optical element and forming a plurality of focal images;
a second condensing-and-reflecting optical element including a plurality of condensing-and-reflecting devices for approximately reversing the direction of travel of the light emitted in the fifth direction by the polarization separating optical element and forming a plurality of focal images;
a reflecting optical element for approximately reversing the direction of travel of the light emitted in the fourth direction by the polarization separating optical element;
a first polarization-state conversion optical element disposed between the polarization separating optical element and the first condensing-and-reflecting optical element;
a second polarization-state conversion optical element disposed between the polarization separating optical element and the second condensing-and-reflecting optical element;
a third polarization-state conversion optical element disposed between the polarization separating optical element and the reflecting optical element; and
a polarization conversion optical element for unifying the direction of polarization of the light emitted in a sixth direction from the polarization separating optical element;
wherein an approximately central axis of a luminous flux, which is reflected by the condensing-and-reflecting devices of the first condensing-and-reflecting optical element and enters the polarization conversion optical element, and an approximately central axis of a luminous flux, which is reflected by the condensing-and-reflecting devices of the second condensing-and-reflecting optical element and enters the polarization conversion optical element, are not parallel to each other, and do not overlap.
In the polarizing illumination device of the present invention, a randomly polarized light beam emitted from the first optical source section is allowed to enter from the first direction of the polarization separating optical element, and is separated into two types of polarized light beams by the first polarization separating film. On the other hand, a randomly polarized light beam emitted from the second light source section is allowed to enter from the second direction of the polarization separating optical element, and is separated into two types of polarized light beams by the second polarization separating film.
Of the thus-separated polarized light beams, the transmitted light, which is emitted in the third direction by the first polarization separating film, passes through the first polarization-state conversion optical element, is reflected by the first condensing-and-reflecting optical element, passes through the first polarization-state conversion optical element again, and travels toward the polarization separating optical element. In this case, this light is separated into a plurality of intermediate luminous fluxes by the first condensing-and-reflecting optical element, and passes through the first polarization-state conversion optical element two times, whereby it is converted into a polarized light beam whose direction of polarization is rotated about 90 degrees. Therefore, this light is reflected by the first polarization separating film, and is emitted in the sixth direction. The polarized light beam emitted in the sixth direction in this way is designated as a first polarized luminous flux.
In addition, the transmitted light, which is emitted in the fifth direction by the second polarization separating film, passes through the second polarization-state conversion optical element, is reflected by the second condensing-and-reflecting optical element, passes through the second polarization-state conversion optical element again, and travels toward the polarization separating optical element. In this case, this light is separated into a plurality of intermediate luminous fluxes by the second condensing-and-reflecting optical element, and passes through the second polarization-state conversion optical element two times, whereby it is converted into a polarized light beam whose direction of polarization is rotated about 90 degrees. Therefore, this light is reflected by the second polarization separating film, and is emitted in the sixth direction. The polarized light beam emitted in the sixth direction in this way is designated as a second polarized luminous flux.
The first and second polarized luminous fluxes each including a plurality of intermediate luminous fluxes form a plurality of focal images on the polarization conversion optical element or in the vicinity thereof. Here, approximately central axes of the first and second polarized luminous fluxes are not parallel to each other, and do not overlap. Therefore, the focal images of the first polarized luminous flux and the focal images of the second polarized luminous flux are formed at positions different from each other. Therefore, the direction of polarization of the first polarized luminous flux and the direction of polarization of the second polarized luminous flux can be unified by the polarization conversion optical element.
On the other hand, the reflected light, which is emitted in the fourth direction by the first polarization separating film and the second polarization separating film, passes through the third polarization-state conversion optical element, is reflected by the third reflecting optical element, passes through the third polarization-state conversion optical element again, and travels toward the polarization separating optical element. In this case, this light passes through the third polarization-state conversion optical element two times, whereby it is converted into a polarized light beam whose direction of polarization is rotated about 90 degrees. Therefore, the light, which is emitted from the first light source section, reflected by the first polarization separating film, and returned to the polarization separating optical element via the third polarization-state conversion optical element and the third reflecting optical element, is reflected by the second polarization separating film, and travels toward the second light source section. In addition, the light, which is emitted from the second light source section, reflected by the second polarization separating film, and returned to the polarization separating optical element via the third polarization-state conversion optical element and the third reflecting optical element, is reflected by the first polarization separating film, and travels toward the first light source section. That is, these light enter the light source sections that are different from those at the time of emission while changing the directions of polarization. Here, a light source section of a projector generally includes a light source lamp and a reflector. Therefore, a polarized light beam, which enters the light source section, is reflected by the reflector of the light source section, is subjected to a rotation action of the polarization axis at that time, and a part of the polarized light beam is converted into a polarized light beam that can pass through a first or a second polarization separating film. In this way, the polarized light beam that can pass through the first or the second polarization separating film, similarly to the above-described polarized light beams emitted in the third and fifth directions, is converted into the first polarized luminous flux or the second polarized luminous flux to enter the polarization conversion optical element, and polarization axes are united. In short, the polarized light beams, which returned to the first and second light source sections from the polarization separating optical element, are finally converted into one type of polarized light beam to be emitted from the polarization conversion optical element.
Therefore, although the two light source sections are used, an area to be illuminated can be equalized to an area to be illuminated by almost one light source section without increasing an incident angle (illumination angle) of illumination light with respect to the illumination area. For this reason, since the amount of light per given illumination angle can be made double that in the case where a single light source section is used, it is possible to illuminate the illumination area very brightly. In addition, since the intermediate luminous fluxes formed by the respective condensing-and-reflecting optical elements are superposed on one illumination area, it is possible to illuminate uniformly the illumination area. Therefore, if the polarizing illumination device of the present invention is used as a light source of a display device, a projection image having extremely uniform brightness can be obtained. Furthermore, according to the polarizing illumination device of the present invention, the randomly polarized light beams emitted from the first and second light source sections can be synthesized into one type of polarized light beam without causing any loss. Therefore, if the polarizing illumination device of the present invention is adopted in a display device using a modulation device of a type that modulates a specific polarized light beam, such as a liquid crystal device, it is possible to obtain an extremely bright projection image.
The positions where the first and second condensing-and-reflecting optical elements are disposed, in this nature, are not clearly defined. In short, the first and second condensing-and-reflecting optical elements may be disposed so that focal images of two polarized light beams included in emitted light of the first and second light source sections (the polarized light beam emitted from the first light source section to pass through the first polarization separating film, and the polarized light beam emitted from the second light source section to pass through the second polarization separating film) are formed at positions spatially separated from each other.
In the present invention, the reflecting optical element may preferably be disposed so that the polarized light beam emitted from the first light source section and reflected by the first polarization separating film, and the polarized light beam emitted from the second light source section and reflected by the second polarization separating film enter the second and first light source sections that are different from those at the time of emission. In particular, when an optical axis of the first light source section and an optical axis of the second light source section perpendicularly intersect, and the polarization separating optical element is a rectangular prism, the reflecting optical element may preferably be disposed to be nearly parallel to a surface of the polarization separating optical element corresponding to the xe2x80x9cfourth directionxe2x80x9d. As a result, the polarized light beam emitted from the first light source section and reflected by the second polarization separating film via the first polarization separating film and the reflecting optical element, and the polarized light beam emitted from the second light source section and reflected by the first polarization separating film via the second polarization separating film and the reflecting optical element can be efficiently allowed to enter the corresponding second and first light source sections, respectively, the utilization efficiency of the polarized light beam can be improved, and the illumination area can be brightly illuminated. Incidentally, the third polarization-state conversion optical element disposed between the polarization separating optical element and the reflecting optical element can be omitted. In this case, both of the polarized light beams reflected by the reflecting optical element and returned to the polarization separating optical element return to their original light source sections from which they are emitted. Since the polarization axes of these polarized light beams are rotated while they are reflected by the reflectors of the light source sections to become polarized light to reach the polarization conversion optical element, these polarized light beams are finally converted into one type of polarized light beam without causing light loss.
In the present invention, an opening shape of each of the condensing-and-reflecting devices can be made similar to the shape of an illumination area. Since light from the light source sections is divided by the condensing-and-reflecting optical elements into a plurality of intermediate luminous fluxes, and finally superposed on the illumination area, the adoption of the above construction can guide the light from the light source sections to the illumination area most efficiently.
In the present invention, a condensing optical element including a plurality of condensing devices is disposed on the side of the incident surface or on the side of the emitting surface of the polarization conversion optical element, in order to condense light emitted from the polarization separating optical element. The disposition of the condensing optical element in this way makes it possible to guide effectively the plurality of intermediate luminous fluxes formed by the condensing-and-reflecting optical elements to predetermined positions of the polarization conversion element while condensing the luminous fluxes. Therefore, an advantage is provided that the polarization conversion efficiency can be increased. When the first and second condensing-and-reflecting optical elements are composed of different numbers of condensing-and-reflecting devices, the condensing optical element may be composed of at least as many condensing devices, or twice as many condensing devices as the number of condensing-and-reflecting devices that constitute the condensing-and-reflecting optical element having the largest number of condensing-and-reflecting devices. However, if the light utilization efficiency of the condensing optical element is regarded as important, the latter construction may preferably be adopted.
In the present invention, a superimposing optical element for superimposing light emitted from the polarization conversion optical element on the illumination area can be disposed on the side of the emitting surface of the polarization conversion optical element. The disposition of the superimposing optical element in this way makes it possible to guide effectively the plurality of intermediate luminous fluxes formed by the condensing-and-reflecting optical elements to the illumination area. Therefore, an advantage is provided that the illumination efficiency can be improved.
In the present invention, an optical-path-changing optical element for changing an optical path of light emitted from the polarization conversion optical element can be disposed on the side of the emitting surface of the polarization conversion optical element. If the optical-path-changing optical element is disposed so that illumination light can be emitted in a direction parallel to a plane defined by optical axes of two light source sections, the thickness of the polarizing illumination device in one direction can be reduced, and a low-profile polarizing illumination device can be realized. Therefore, when the polarizing illumination device is used as a light source of a projector or the like, a compact projector can also be obtained.
In the present invention, each of the condensing-and-reflecting devices of the first and second condensing-and-reflecting optical elements can be formed of a plurality of curved-surface reflecting mirrors. In addition, each of the condensing-and-reflecting devices of the first and second condensing-and-reflecting optical elements can be composed of a lens, and a reflecting surface provided on a surface of the lens opposite to the polarization separating optical element. With this construction, light from the light source sections can be easily divided into a plurality of intermediate luminous fluxes. Here, if the curved-surface reflecting mirrors are formed of decentering mirrors, or if the lens is formed of a decentering lens, the above-described polarization conversion optical element and the condensing optical element can be reduced in size, and the light can be effectively guided to the illumination area without using the above-described superimposing optical element.
The polarizing illumination device according to the present invention can be used in a projector having an optical modulation device for modulating light emitted from the polarizing illumination device, and a projection optical system for projecting the light modulated by the optical modulation device.
Furthermore, the polarizing illumination device according to the present invention can be used in a projector which has a color-light-separating optical element for separating light emitted from the polarizing illumination device into a plurality of color light, a plurality of optical modulation devices for modulating each of the color light separated by the color-light-separating optical element, a color-light-synthesizing optical element for synthesizing the light modulated by the plurality of optical modulation devices, and a projection optical system for projecting the light synthesized by the color-light-synthesizing optical element, and which can display a color image.
In addition, the polarizing illumination device according to the present invention can be used in a projector having a reflective optical modulation device for modulating light emitted from the polarizing illumination device, a polarization separating optical element for separating a plurality of polarized light components included in the light emitted from the polarizing illumination device and the light modulated by the reflective optical modulation device, and a projection optical system for projecting the light modulated by the reflective optical modulation device and emitted via the polarization separating optical element.
Furthermore, the polarizing illumination device according to the present invention can be used in a projector which has a plurality of reflective optical modulation devices for modulating light emitted from the polarizing illumination device, a polarization separating optical element for separating a plurality of polarized light components included in the light emitted from the polarizing illumination device and the light modulated by the plurality of reflective optical modulation devices, a color-light-separating-and-synthesizing optical element disposed between the polarization separating optical element and the plurality of reflective optical modulation devices, for separating light emitted from the polarizing illumination device into a plurality of color light and synthesizing the color light emitted from the plurality of reflective optical modulation devices, and a projection optical system for projecting the light modulated by the reflective optical modulation devices and emitted via the color-light-separating-and-synthesizing optical element and the polarization separating optical element.
In addition, the polarizing illumination device according to the present invention includes a color-light-separating optical element for separating light emitted from the polarizing illumination device into a plurality of color light, a plurality of reflective optical modulation devices for modulating each of color light separated by the color-light-separating optical element, a plurality of polarization separating optical elements for separating a plurality of polarized light components included in each of the color light separated by the color-light-separating optical element and in each of the color light modulated by the plurality of reflective optical modulation devices, a color-light-synthesizing optical element for synthesizing the light modulated by each of the reflective optical modulation devices and emitted via each of the polarization separating optical element, and a projection optical system for projecting the light synthesized by the color-light-synthesizing optical element, and can also be used in a projector.
In this way, when a projector using the polarizing illumination device of the present invention, a bright, and uniformly bright projection image can be obtained. Since the polarizing illumination device of the present invention emits luminous fluxes polarized in the same direction, it is suitable for a projector using liquid crystal devices as optical modulation devices.
In the above-described projector, at least one of the first and second light source sections may preferably be detachably constructed. With this construction, one of the light source sections can be detached when the projector is carried, thereby improving portability.
In addition, in the above-described projector, at least one of the first and second light source sections may preferably be selectively lit. With this construction, for example, when the projector is driven by a battery, the longevity of the battery can be extended by selectively lighting only one of the light sources. In addition, the brightness of a projection image can be appropriately changed according to the environment, or according to the preferences of the viewer such that two light source sections are lit when the projection image is viewed in a light place, and only one of them is selectively lit when the projection image is viewed in a dark place.
Furthermore, in the above-described projector, spectral characteristics and brightness characteristics of light emitted from the first and second light source sections can be allowed to differ from each other. With this construction, the hue of the illumination light can be easily set to a predetermined hue.